1. Field of the Invention
The present invention relates to a touch sensor using optical fibers.
2. Description of Related Art
Japanese Kohyo (PCT) Patent Publication No. 2002-507279 discloses a touch sensor in which many pairs of optical fibers are disposed in an elastic member such as urethane foam. In the touch sensor, two optical fibers, that is, a light-emitting optical fiber and a light-receiving optical fiber, are disposed at each pressure sensing point. The front ends of the light-emitting and light-receiving optical fibers are close to each other in the vicinity of the pressure sensing point. In the touch sensor, when a portion of the elastic member corresponding to a pressure sensing point is bent due to a force externally applied, the luminance of the light being emitted from the front end of the light-emitting optical fiber changes in accordance with the magnitude of the force. By using this characteristic, the force applied to the pressure sensing point is detected. In a similar touch sensor, a single optical fiber is disposed at each pressure sensing point. In the touch sensor, the single optical fiber serves as both of light-emitting and light-receiving optical fibers. A beam splitter is used to separate the direction of the incident light and the direction of the reflected light at an end of each optical fiber.
In the touch sensor in which a single optical fiber is disposed at each pressure sensing point, the manufacturing cost can be reduced because the number of optical fibers required is small. In addition, there is no need of setting light-emitting and light-receiving optical fibers at each pressure sensing point such that their front ends are close to each other. This simplifies the manufacturing process and improves the sensor accuracy. In the touch sensor, however, the use of the beam splitter brings about an increase in the manufacturing cost and a complicated sensor construction.